linux-kernel - Re: [PATCH] Work around for enabling CONFIG

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Message-Id: <57E4AC5C.5010803@linux.vnet.ibm.com>
Date:   Fri, 23 Sep 2016 09:45:24 +0530
From:   Akshay Adiga <akshay.adiga@...ux.vnet.ibm.com>
To:     Michael Ellerman <mpe@...erman.id.au>,
        linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Cc:     anton@...ba.org
Subject: Re: [PATCH] Work around for enabling CONFIG_CMDLINE on ppc64le

Hi Michael,

Anton found this bug and raised it against gcc v7.0 and a fix is available
  in upstream gcc.

	https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71709

Currently, gcc v5.4.0  and v6.1.1 shipped with Ubuntu 16.04 and 16.10  respectively,
  are hitting this problem.

I have also raised bug against Ubuntu for fixing gcc for 16.04.

https://bugzilla.linux.ibm.com/show_bug.cgi?id=146668


On 09/22/2016 03:51 PM, Michael Ellerman wrote:
> Akshay Adiga <akshay.adiga@...ux.vnet.ibm.com> writes:
>
>> Observed that boot arguments (passed as CONFIG_CMDLINE)  are not being
>> picked up by kernel while using gcc-ppc64-linux-gnu v5.4.0 and v6.1.1.
>> While it works as expected with v5.3.1 .
>>
>> Found that in init/main.c in  setup_command_line() the pointers passed to
>> strcpy() is messed up.
> Hi Akshay,
>
> Thanks for debugging this.
>
>> The problem goes away when compiler optimization is restricted to -O1.
>> diff --git a/init/main.c b/init/main.c
>> index a8a58e2..4259c42 100644
>> --- a/init/main.c
>> +++ b/init/main.c
>> @@ -358,7 +358,13 @@ static inline void smp_prepare_cpus(unsigned int maxcpus) { }
>>    * parsing is performed in place, and we should allow a component to
>>    * store reference of name/value for future reference.
>>    */
>> -static void __init setup_command_line(char *command_line)
>> +static void __init
>> +#ifdef CONFIG_PPC64
>> +	#if  GCC_VERSION > 50301
>> +		__attribute__((optimize("-O1")))
>> +	#endif
>> +#endif
>> +		setup_command_line(char *command_line)
>>   {
>>   	saved_command_line =
>>   		memblock_virt_alloc(strlen(boot_command_line) + 1, 0);
> But I can't merge that patch.
>
> Our options are one or both of:
>   - get GCC fixed and backport the fix to the compilers we care about.
>   - blacklist the broken compiler versions.
>
> Is there a GCC bug filed for this?
>
> cheers
>